Sheet abrasive and method of making the same



Patented Oct. 22, 1940 PATENT OFFICE SHEET ABRASIVE AND METHOD OF MAKINGTHE SAME Francis Gurney Okie, St. Paul, Minn.,'assignor to MinnesotaMining 8; Manufacturing Company, St. Paul, Minn., a corporation ofDelaware No Drawing. Original application February 6,

1929, Serial No. 338,022. plication April 28, 1933, Serial No. 668,384.

newed October 25, 1939 6 Claims.

My present invention relates in general to the treatment of material,preferably in sheet form, andmore particularly the treatment of materialfor the purpose of forming or attaining composite structures, of whichwell known forms of abrasives such as what is commonly known assandpaper is an example.

Although I hereinafter disclose the practice of my invention inconnection with abrasives such as sandpaper, it will be understood thatmy invention, or certain features thereof, have a wider field ofutility.

Composite structures of the abrasive type such as sandpaper or emerycloth comprise generally (a) a base of sheet material, which may befelted as in the case of paper or woven as in the case of cloth, (1)) amore or less finely comminuted resistant material having abradingproperties, such as garnet or corundum, and (c) a binder generally inthe form of a glue which serves to bind the abrasive to the base.

The principal objects of my present invention reside in the provision ofa binder which functions more efliciently than any known to me, that is,the abrasive article, including the binder disclosed herein and thebacking or base of the abrasive article is tougher whether used dry orin a water abrading operation; the provision of an abrasive articlehaving the characteristics hereinafter set forth which gives a betterperformance in use when employed in water abrading operations, is a morewaterproof article and in which there is less slipperiness of thebacking, thereby permitting the operator to maintain a better grip onthe sheet when rubbing surfaces; the provision of an improved flexiblewaterproof abrasive article characterized by extensibility andcompressibility to accommodate itself to bending when in use; theprovision of such an article wherein the desired adhesive action betweenthe binder and the backing is materially increased; the provision of animproved binder and abrasive article wherein a good balance of drying isattained without any tendency to crack when dry; the provision of animproved abrasive article wherein the backing or sheet is adequatelypermeated with the waterproofing medium which prevents the water orother liquid employed in wet sanding from entering the pores andeventually cause swelling of the backing, thereby maintaining theoriginal body much longer than in any flexible abrasive article known tome; the provision of improved coatings which tend to inscopic,permeative,

Divided and this apcrease the life of the paper in use withoutmaterially decreasing the flexibility of the same when dry; theprovision of an improved binding and sizing material which has moistureproofing characteristics and is flexible when dry.

This invention in one of its forms further includes the improvementwhich resides in incorporating soft oils in the backing or sheet insufficient quantity to load the sheet but in a degree insuflicient toresult in rendering the sheet brittle when dry, in combination with asealing coat on the surface to increase the waterproofness of the sheetand wherein the employment of a harder binding coat when dry iscompensated for by the inclusion in the sheet of a waterproofed materialwhich maintains the flexibility of the binder and the sheet but resultsin the provision of a backing having greater resistance to abrasion,that is,

to breaking down of the binder when employed in a wet sanding or waterabrading operation.

In the employment of my present invention for the production of aflexible abrasive article, such for example, as sandpaper and the like,suitable for employment in a wet sanding operation (which I cite forpurposes of example) I employ as the base, a sheet of material (whichmay be paper, cloth or the like) of such texture and thickness as willconveniently serve the employment contemplated, and as the abrasive suchcomminuted material (which may be crushed garnet) similarly adapted toserve the function in view,

together with the binder hereinafter referred to.

in detail for attaching the grits to the paper; and suitable auxiliarycoatings within and without the paper sheet which have characteristicswhich render the bond between the grit and the sheet highly tenaciousand result in a relatively hard finish without materially detractingfrom the flexibility of the abrasive article when dry.

It is, of course, desirable that the binder utilized have the functionsand characteristics not only of great mechanical strength and of greatbinding strength, but also that it be non-hygromoisture resistant,easily worked, readily obtainable, relatively inexpensive and capable offacile application to the sheet.

In the manufacture of waterproof abrasive sheets, I have treated thebacking or sheet with a waterproofing solution and then applied coats ofbinder and grit, together with auxiliary coating or coatings on the backof the sheet or on both the back and front. The degree of resistance topermeation'by water or other liquid emtemal pressure.

ployed in a wet sandins operation depends in part on the amount ofwaterproofed materials put into the sheet, and in part upon the degreeof drying to which the materials employed are subjected, which in otherflexible abrasive articles have made it necessary first to attain afairly good drying of the auxiliary back sizing in order to.

give high resistance to abrasion in the backing, that is, to prevent thepaper wearing of! the back when the operator is rubbing a surface in awet sanding operation, and, though a highly efllclent ,result' isobtained in such articles, these do not have the desired high resistanceto abrasion of the backing characterizing the present invention.

If, under the other methods known to me, a harder auxiliary coatingmaterial is employed,

this results in stiflening the sheet beyond the ficient flexibility ofthe sheet when the grit is.

[applied so that the cooperation of the preliminary paper treatment andsizing coats with the sheet and the bonding coat result in a balance offlexibility, together with an increase in external hardness of thesheet.

In making the new abrasive article of this invention, I prefer to applya relatively thin top or front coat as a presizing designed not topermeate the sheet materially but serving as a penetration controllingcoat when the binder coat is applied. I then apply the binder coat; thenthe grit. I then apply in succession two relatively soft coats to theback of the sheet, that is, to the side opposite to the grit. I preferthat the second auxiliary back sizing coat be of a softer material whenset than that of the first back sizing coat so as to not materiallydetract from the flexibility of the finished product, sandpaper.

To sum up, after the sheet has been treated, and, therefore, includes abacking, presized on the front, that is, having at least one frontpresizing coat, the primary binding coat is applied to the front of thesheet, and before this coat becomes set or dry. a layer of the grits isdeposited thereon, preferably without the application of ex- Then Iapply the backsizing coats and a sand sizing coat, that'is, a coat isapplied over the grits and primary binding coat for compensating for anyabsorption of the primary binder by the base or backing. The sheet isthen, when dry, ready for use. The sheet may, for some purposes, at theoutset, though not necessarily, contain soft oils tending to render thesheet itself waterproof.

From the foregoing, it will be seen that the abrasive sheet, with all ofthe advantages of this invention, includes the following principalelements: a treated sheet which may contain soft oils in such amount asto render the sheet substantially waterproof; a presizing front coat; abinding grit carrying coat; one or more backsizing coats which preventthe entrance of water into the back of the sheet where the operatorshand comes in contact; and a sand sizing coat applied to said bindingcoat and grit where desirable or necessary.

It is preferable that the sand sizing coat and grit binding coat berelatively hard when dry; and that the backsizing coats be soft. It willthus be seen that a relatively hard outer surface is attained which willprotect the binder coat and yet not materially detract from itsflexibility and that the soft oils in the sheet when employed willpermit of afiexing of the sheet without a tendency to when dry that isavailable for my purposes, and

which does not crack when dry; a presizing designed to controlpenetration of these hard oils into the backing, the primary backsizingcoat is of a soft material and the second coat of backsizing is of sucha soft material that when placed on a glass it may be scraped off withthe finger-nail several days after application.

In this way, I am enabled to provide for elon- Y gation of the backingwhich will prevent the finishing article from becoming brittle, orcracking when bent.

In carrying out the process of manufacturing the improved abrasivearticle of this invention, which process I believe to be new, and inorder to obtain the proper drying cycle and to reduce the time required,I prefer to apply both coats of the backsizing in the second operation,that is, for example, the coated sheet is passed through a set ofsqueeze rolls which apply oil on the backside and then the sealing coatis applied thereto. Instead of sending it two trips through the steps ofreceiving two backsizing coats, I apply both coats of backsizing in thesecond operation. The second coat of the backsizing thus seals thesurface so that oxidation is retarded in the center of the fibrecellulose sheet.

In the present invention, I find that it is possible to employ a clearbinder for retaining the grits, that is, the employment of a pigment inthe binder to control penetration into the paper stock is not necessary,and I find that in the employment of a clear binder, when properlycontrolled, substantially all the strength of the adhesive therein maybe used in retaining the grits.

The employment of a presizing coat on the sheet beneath the binder coatprevents an undue penetration of the sheet by the clear binder. I havefound that I can obtain control of the application of the clear binderso as to prevent its undue penetration into the sheet by applying thebinder to raw paper stock, which has been presized on the face but notpreviously backsized. I have found that in doing this, less penetrationof the sheet by the grit binding coat takes place, probably due to thefact that in the prior operations known to me, the backsizing thinners,in evaporating, apparently exert a suction or capillary action on thebinder applied to the opposite side of the sheet to hold grits and thustend to pull the binder into the sheet.

In applying the various coatings by my preferred process which preventsthe undue penetration of the sheet by the clear binder, I preferablyfirst presize the paper and then apply the clear animus 3 meate thewhole drying room. The major portion of the oven has a' temperature ofabout 125 F. to

130 1". After this trip through the oven, the two backsizing coats andthe sandsizing coat are aps plied, and the paper again passed one tripthrough an oven, maintaining substantially the same temperature cycle asin its first trip.

In order to give the hard finish to the paper, the sandsizing coat isapplied before the second oven. In the article that passes two tripsthrough an oven, the presizing coat, clear binder and sand are on thepaper on the first trip, and the two ,backsizing coats and thesandsizing coat are applied to the paper for 'its second trip 16 throughthe oven.

I have discovered that natural or synthetic, having the desiredcharacteristics such, for example, as rosin and other gums and resins,perform the functions desired,

20 that is, of giving the necessary mechanical strength for abrasionoperations and binding strength by compatibility to the abrasive andwaterproofness which produces a binder suitable for my purposes, whenemployed with a 20 suitable vehicle.

In preparing the binder for use, the gum or resin is employed inconnection with a suitable vehicle which I prefer is of the type such,for example, as China-wood oil, linseed oil, or both.

Certain other oils, such as semi-drying oil (soyabean oil) are suitablefor that purpose.

In employing the gum or resin prepared with a vehicle such, for example,as China-wood oil, to one surface of the base or backing, I have foundthat the action of a vehicle involves a penetration of the base and, insome instances, this results in a weakening of the binding action and,while not sufiicient to destroy the usefulness of the binder for somepurposes, it is un- 0 desirable. My experience with this binder hasshown that the application of a sizing coat to the back of the sheettends to create a suction or capillary action and in order to prevent anundue penetration, in other inventions I have employed a. fillerfor.preventing a too great penetration into the backing. However, byomitting the backsizing coats until after the binder is applied andfairly dry, I am enabled to employ a clear binder without the necessityof incorporating ingredients for preventing undue penetration. Thisfunction is further attained by the employment of a presize, that is, asizing coat which is applied to one side of the sheet which is toreceive the binder.

5 In my preferred practice in the production of this invention I employpresizes depending on the absorbency characteristics of the paper andthe fluidity of the binder.

For dense papers, which do not absorb readily,

m the following examples of solutions used are representative.

gums and resins,

Preferred Example No. 2

Parts Oleum spirits 96.0 Metal soaps, such as aluminum stearate,

aluminum, palmitate. magnesium ole- 5 ate, etc 4.0

For papers which are quite absorbent, or to control more fiuid binders,a pigment may be added to such solutions as represented in Ex m amplesNo. 1 and No. 2.

A representative formula for a presizing solution containing a pigmentis as. follows:

Parts Formula No. 1 45 Formula N0. 2 45 Blanc fixe (magnesium silicateor the like)..- 10

For papers which are very absorbent I use a It is not intended that Ishould limit myself to the use of the above to obtain a great degree 30of finesse in the presizing principle.

I have further found that solutions such as cellulose acetate orcellulose acetate combined with other oils; other metal soap, such ascalcium oleate, and the like; and combinations of 35 these solutions,with pigment such as magnesium carbonate, blanc fixe, magnesiumsilicate, and the like; and synthetic resin solutions, such as phenolformaldehyde resins, may be used, depending on degree of control ofbinder penetra- 0 tion desired, and varying absorbency qualities ofpaper stock used.

One of the virtues of the presize is that it prepares the surface of thesheet to receive the clear binder and which tends to prevent undue 4,5penetration and, as well, serves to seal the front side of the sheet ina manner similarly to the backsize, which is applied later, to seal theopposite side.

In my preferred employment of a clear binder 50 the same may include thefollowing ingredients in proportions by parts:

The sandsizing coat is applied over the grits 76 and binder and for mypurposes may include the ingredients'in parts as follows:

General Parts Vegetable drying oils 34 Resin 13 Lime 0.2 Manganese oxide0.04 Litharge 0.09 Lead acetate 0.04 Cobalt acetate 0.001 Oleum 45.629Turpentine 7.0

Preferred Parts China-wood oil 34 Rosin 5.0 Ester gum 8.0 Lime 0.2Manganese oxide 0.04 Litharge 0.09 Lead acetate 0.04 Cobalt acetate0.001 Oleum 45.629 Turpentine 7.0

The back sizing coat which is softer than either the clear binder or thehard external sand sizing coat may include the following ingredients byparts:

The auxiliary back sizing coat, that is, the second coat applied to theback of the sheet, may include the following ingredients by parts:

General Parts Nitrocellulose sec.) 8.8 Vegetable drying oil 13.2 Oleum29.0 Nitrocellulose solvent 25.5

Ground silica 17.0 Resin 4.5

Water 2.0 Plasticizer or softener.

Second back sizing solutions may include the parts as in the formulahereinafter.

Parts Nitrocellulose 9.4 Raw or heat treated China-wood oil 10.5 Raw orblown castor oil 2.7 Ester gum 3.8 Silica 19.5 Water 1.5 Butylcellosolve 24.0 Mineral spirits 28.6

From the foregoing, it will be understood that the pre-size may includefillers for preventing penetration where it is desired to first backsize the paper, that is, apply the back sizing coats in the formulae Dand E, before applying the binder.

After the pre-size, clear binder adhesive and sand have been applied tothe paper, the articleis suitably forced dried, that is, partiallybaked, as it is said, to the desired extent by subjecting it in theusual manner to a temperature which I prefer to control at approximatelyabout to F., depending upon the degree of hardness desired, and for arequired period of time, preferably 36 to 48 hours. It will be obviousthat the hardness of finish of the article may be varied as desired byobtaining variations in the tempera ture employed and the time which thearticle is subjected to heat.

The back sizing coats of the formulae D and E and the hard and size coatof formula C are then applied, and the article again subjected to thedesired hardening temperature which may be the same as that previouslypointed out.

This application is a division of my application Serial No. 338,022,filed February 6, 1929, noW Patent No. 2,013,925 issued September 10,1935. Reference is also made to my application Serial No. 755,445 filedNovember 30, 1934, now Patent No. 2,169,277 issued August 15, 1939 andto my application Serial No. 213,519 filed June 13, 1938 as a divisionof the present case, in which other phases of my invention are claimed.

Having thus described my invention and illustrated its use, what I claimas new and desire to secure by Letters Patent is:

1. A composition for forming a sizing coat comprising a cellulose esterabout 7.2 to about 9.4 parts, a drying oil about 8.0 to about 13.2parts, resins about 2.5 to about 4.5 parts, with mixed solvents for thewater-proofing materials.

2. A composition in accordance with claim 1 containing about 2.5 toabout 2.7 parts of a plasticizer taken from the group consisting ofcastor oil, raw castor oil, blown castor oil.

3. A composition in accordance with claim 1 containing about 17 to about19.5 parts of a mild friction increasing material comprising silica.

4. The composition for forming a sizing coating comprising celluloseester about 8.8 parts, drying oil about 13.2 parts, resins about 4.5parts, mild friction increasing material comprising silica about 17parts and mixed solvents for the waterproofing materials.

iii)

5. The composition for forming a sizing coating comprisingnitrocellulose about 9.4 parts, China-wood oil about 10.5 parts, blowncastor oil about 2.7 parts, ester gum about 3.8 parts, mild frictionincreasing material comprising silica about 19.5 parts and a mixedsolvent for the waterproofing materials.

6. The composition for forming a sizing coating, comprisingnitro-cellulose about 7.2 parts, a. drying oil about 8 parts, blown oilabout 2.5 parts, ester gum about 2.5 parts, the composition includingmixed solvents for the ingredients afore- 6 mentioned.

FRANCIS GURNEY OKIE.

